A mold clamping unit of an injection molding machine includes a base fixed to a bed or a substructure, a fixed platen fixed onto the base, a pressure receiving platen (or a mold clamping cylinder) disposed parallel with the fixed platen on the base, a tie bar disposed across the fixed platen and the pressure receiving platen, and a movable platen disposed between the fixed platen and the pressure receiving platen and moving on the base while being guided by the tie bar.
The movable platen and the fixed platen are used to clamp a mold.
The base used in the mold clamping unit is required to be rigid enough to withstand mold clamping reaction force. A highly rigid base structure disclosed in JP 3631906 B, for example, is known.
The base structure disclosed in JP 3631906 B will be described with reference to FIGS. 9 and 10.
As illustrated in FIG. 9, a base 100 for an injection molding machine includes a lower flat plate 101, two H-beams 102, 103 disposed on the lower flat plate 101, reinforcing members 104, 105 sandwiched by the H-beams 102, 103, and an upper flat plate 106 disposed on the two H-beams 102, 103. These constituent elements 101 to 106 are joined together by welding or with bolts.
FIG. 10 illustrates the base 100 for an injection molding machine after the joining by welding or with bolts.
The reinforcing member 104 on the nearer side to the viewer in the drawing can be joined to the two H-beams 102, 103 by welding because a welding rod is placed from the nearer side.
On the other hand, it is difficult to join the reinforcing member 105 on the farther side because the reinforcing member 104 on the nearer side is obstructive. For example, the reinforcing member 105 is preliminarily joined to one H-beam 102. The other H-beam 103 is adjusted in position with respect to the reinforcing member 105. The H-beam 103 is fixed to the reinforcing member 105 with bolts. With these processes, the reinforcing member 105 on the farther side can be attached.
These processes require a bolt fastening step in addition to a welding step, resulting in an increase in the number of steps. An increase in the number of steps increases manufacturing cost.
The bolts used for fixing loosen inevitably and are thus required to be fastened periodically. This increases maintenance and inspection cost.
To reduce manufacturing cost and maintenance and inspection cost, it is desired to fix the constituent elements only by welding.
As illustrated in FIG. 9, the H-beam 102 includes a lower flange 102a, an upper flange 102b, and a web 102c connecting these flanges, and similarly, the H-beam 103 includes a lower flange 103a, an upper flange 103b, and a web 103c connecting these flanges.
As illustrated in FIG. 10, the lower flat plate 101 lies on the lower flanges 102a, 103a, and the upper flat plate 106 lies on the upper flanges 102b, 103b. This configuration causes overlapping of members.
The upper flat plate 106 is applied with a downward load and is thus required to have rigidity especially at the center. The center of the upper flat plate 106 is not covered with the upper flanges 102b, 103b, so that support with the upper flanges 102b, 103b cannot be expected. As a measure, the upper flat plate 106 is required to be thickened to enhance rigidity. This results in a heavier upper flat plate 106 in addition to the overlapping members.
Since the known base 100 is rigid but heavy, it is desired to reduce the weight of the base 100, considering manufacturing and transportation costs.
As a substitute for the base for an injection molding machine disclosed in JP 3631906 B, a base for an injection molding machine is needed in which constituent elements can be fixed only by welding and that has light weight on the precondition that a plurality of webs are included.